[PATCH v3 14/28] Add new computed struct value callback interface
Lancelot SIX
lsix@lancelotsix.com
Tue Oct 26 22:50:01 GMT 2021
Hi,
As for previous patches, I have included (minor) comments below.
On Thu, Oct 14, 2021 at 10:32:21AM +0100, Zoran Zaric via Gdb-patches wrote:
> From: Zoran Zaric <Zoran.Zaric@amd.com>
>
> At this point all support is there to add a new callback interface
> for the computed struct value infrastructure.
>
> Original callback interface (piece closure) is going to be removed as
> soon as the switch to the new DWARF entry classes is done in the next
> few patches.
>
> gdb/ChangeLog:
>
> * dwarf2/expr.c (class computed_closure): New class.
> (closure_value_funcs): New closure callback structure.
> (copy_value_closure): New function.
> (free_value_closure): New function.
> (rw_closure_value): New function.
> (check_synthetic_pointer): New function.
> (write_closure_value): New function.
> (read_closure_value): New function.
> (is_optimized_out_closure_value): New function.
> (indirect_closure_value): New function.
> (coerce_closure_ref): New function.
> ---
> gdb/dwarf2/expr.c | 307 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 307 insertions(+)
>
> diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
> index 1b6622d5f59..e33be7e7c1c 100644
> --- a/gdb/dwarf2/expr.c
> +++ b/gdb/dwarf2/expr.c
> @@ -323,6 +323,92 @@ class dwarf_location;
> class dwarf_memory;
> class dwarf_value;
>
> +/* Closure callback functions. */
> +
> +static void *
> +copy_value_closure (const value *v);
> +
> +static void
> +free_value_closure (value *v);
> +
> +static void
> +rw_closure_value (value *v, value *from);
> +
> +static int
> +check_synthetic_pointer (const value *value, LONGEST bit_offset,
> + int bit_length);
> +
> +static void
> +write_closure_value (value *to, value *from);
> +
> +static void
> +read_closure_value (value *v);
> +
> +static bool
> +is_optimized_out_closure_value (value *v);
> +
> +static value *
> +indirect_closure_value (value *value);
> +
> +static value *
> +coerce_closure_ref (const value *value);
> +
> +/* Functions for accessing a variable described by DW_OP_piece,
> + DW_OP_bit_piece or DW_OP_implicit_pointer. */
> +
> +static const lval_funcs closure_value_funcs = {
> + read_closure_value,
> + write_closure_value,
> + is_optimized_out_closure_value,
> + indirect_closure_value,
> + coerce_closure_ref,
> + check_synthetic_pointer,
> + copy_value_closure,
> + free_value_closure
> +};
> +
> +/* Closure class that encapsulates a DWARF location description and a
> + frame information used when that location description was created.
> + Used for lval_computed value abstraction. */
> +
> +class computed_closure : public refcounted_object
> +{
> +public:
> + computed_closure (std::unique_ptr<dwarf_location> location,
> + struct frame_id frame_id)
> + : m_location (std::move (location)), m_frame_id (frame_id)
> + {}
> +
> + computed_closure (std::unique_ptr<dwarf_location> location,
> + struct frame_info *frame)
> + : m_location (std::move (location)), m_frame (frame)
> + {}
> +
> + const dwarf_location &get_location () const;
Is there a reason not to inline this function definition as well? It
seems as trivial as get_frame_id and get_frame.
> +
> + frame_id get_frame_id () const
> + {
If I understand correctly, m_frame_id and m_frame are mutually
exclusive. To be on the safe side, I would be tempted to add a check
here:
gdb_assert (m_frame == nullptr);
> + return m_frame_id;
> + }
> +
> + frame_info *get_frame () const
> + {
> + return m_frame;
> + }
> +
> +private:
> + /* Entry that this class encloses. */
> + const std::unique_ptr<const dwarf_location> m_location;
> +
> + /* Frame ID context of the closure. */
> + frame_id m_frame_id;
> +
> + /* In the case of frame expression evaluator the frame_id
> + is not safe to use because the frame itself is being built.
> + Only in these cases we set and use frame info directly. */
> + frame_info *m_frame = NULL;
I guess nullptr is prefered over NULL (across the patch).
> +};
> +
> /* Base class that describes entries found on a DWARF expression
> evaluation stack. */
>
> @@ -524,6 +610,11 @@ class dwarf_location : public dwarf_entry
>
> using dwarf_location_up = std::unique_ptr<dwarf_location>;
>
> +const dwarf_location &computed_closure::get_location () const
> +{
> + return *m_location;
> +}
> +
> void
> dwarf_location::read_from_gdb_value (frame_info *frame, struct value *value,
> int value_bit_offset,
> @@ -1594,6 +1685,222 @@ dwarf_composite::is_optimized_out (frame_info *frame, bool big_endian,
> return false;
> }
>
> +static void *
> +copy_value_closure (const value *v)
> +{
> + computed_closure *closure = ((computed_closure*) value_computed_closure (v));
> +
> + if (closure == nullptr)
> + internal_error (__FILE__, __LINE__, _("invalid closure type"));
> +
> + closure->incref ();
> + return closure;
> +}
> +
> +static void
> +free_value_closure (value *v)
> +{
> + computed_closure *closure = ((computed_closure*) value_computed_closure (v));
> +
> + if (closure == nullptr)
> + internal_error (__FILE__, __LINE__, _("invalid closure type"));
> +
> + closure->decref ();
> +
> + if (closure->refcount () == 0)
> + delete closure;
> +}
> +
> +/* Read or write a closure value V. If FROM != NULL, operate in "write
> + mode": copy FROM into the closure comprising V. If FROM == NULL,
> + operate in "read mode": fetch the contents of the (lazy) value V by
> + composing it from its closure. */
> +
> +static void
> +rw_closure_value (value *v, value *from)
> +{
> + LONGEST bit_offset = 0, max_bit_size;
> + computed_closure *closure = (computed_closure*) value_computed_closure (v);
> + bool big_endian = type_byte_order (value_type (v)) == BFD_ENDIAN_BIG;
> + const dwarf_location &location = closure->get_location ();
> +
> + if (from == NULL)
> + {
> + if (value_type (v) != value_enclosing_type (v))
> + internal_error (__FILE__, __LINE__,
> + _("Should not be able to create a lazy value with "
> + "an enclosing type"));
> + }
> +
> + ULONGEST bits_to_skip = HOST_CHAR_BIT * value_offset (v);
> +
> + /* If there are bits that don't complete a byte, count them in. */
> + if (value_bitsize (v))
> + {
> + bits_to_skip += HOST_CHAR_BIT * value_offset (value_parent (v))
> + + value_bitpos (v);
> + if (from != NULL && big_endian)
> + {
> + /* Use the least significant bits of FROM. */
> + max_bit_size = HOST_CHAR_BIT * TYPE_LENGTH (value_type (from));
> + bit_offset = max_bit_size - value_bitsize (v);
> + }
> + else
> + max_bit_size = value_bitsize (v);
> + }
> + else
> + max_bit_size = HOST_CHAR_BIT * TYPE_LENGTH (value_type (v));
> +
> + frame_info *frame = closure->get_frame ();
> +
> + if (frame == NULL)
> + frame = frame_find_by_id (closure->get_frame_id ());
> +
> + if (from == NULL)
> + {
> + location.write_to_gdb_value (frame, v, bit_offset, bits_to_skip,
> + max_bit_size - bit_offset, 0);
> + }
> + else
> + {
> + location.read_from_gdb_value (frame, from, bit_offset, bits_to_skip,
> + max_bit_size - bit_offset, 0);
> + }
> +}
> +
> +static void
> +read_closure_value (value *v)
> +{
> + rw_closure_value (v, NULL);
> +}
> +
> +static void
> +write_closure_value (value *to, value *from)
> +{
> + rw_closure_value (to, from);
> +}
> +
> +/* Check if a closure value V contains describes any piece
One of 'contains' and 'describes' might be too much here I guess.
Best,
Lancelot.
> + of the underlying location description as optimized out. */
> +
> +static bool
> +is_optimized_out_closure_value (value *v)
> +{
> + LONGEST max_bit_size;
> + computed_closure *closure = (computed_closure*) value_computed_closure (v);
> + bool big_endian = type_byte_order (value_type (v)) == BFD_ENDIAN_BIG;
> + const dwarf_location &location = closure->get_location ();
> +
> + if (value_type (v) != value_enclosing_type (v))
> + internal_error (__FILE__, __LINE__,
> + _("Should not be able to create a lazy value with "
> + "an enclosing type"));
> +
> + ULONGEST bits_to_skip = HOST_CHAR_BIT * value_offset (v);
> +
> + /* If there are bits that don't complete a byte, count them in. */
> + if (value_bitsize (v))
> + {
> + bits_to_skip += HOST_CHAR_BIT * value_offset (value_parent (v))
> + + value_bitpos (v);
> + max_bit_size = value_bitsize (v);
> + }
> + else
> + max_bit_size = HOST_CHAR_BIT * TYPE_LENGTH (value_type (v));
> +
> + frame_info *frame = closure->get_frame ();
> +
> + if (frame == NULL)
> + frame = frame_find_by_id (closure->get_frame_id ());
> +
> + return location.is_optimized_out (frame, big_endian, bits_to_skip,
> + max_bit_size, 0);
> +}
> +
> +/* An implementation of an lval_funcs method to see whether a value is
> + a synthetic pointer. */
> +
> +static int
> +check_synthetic_pointer (const value *value, LONGEST bit_offset,
> + int bit_length)
> +{
> + LONGEST total_bit_offset = bit_offset + HOST_CHAR_BIT * value_offset (value);
> +
> + if (value_bitsize (value))
> + total_bit_offset += value_bitpos (value);
> +
> + computed_closure *closure
> + = (computed_closure *) value_computed_closure (value);
> +
> + return closure->get_location ().is_implicit_ptr_at (total_bit_offset,
> + bit_length);
> +}
> +
> +/* An implementation of an lval_funcs method to indirect through a
> + pointer. This handles the synthetic pointer case when needed. */
> +
> +static value *
> +indirect_closure_value (value *value)
> +{
> + computed_closure *closure
> + = (computed_closure *) value_computed_closure (value);
> +
> + struct type *type = check_typedef (value_type (value));
> + if (type->code () != TYPE_CODE_PTR)
> + return NULL;
> +
> + LONGEST bit_length = HOST_CHAR_BIT * TYPE_LENGTH (type);
> + LONGEST bit_offset = HOST_CHAR_BIT * value_offset (value);
> +
> + if (value_bitsize (value))
> + bit_offset += value_bitpos (value);
> +
> + frame_info *frame = get_selected_frame (_("No frame selected."));
> +
> + /* This is an offset requested by GDB, such as value subscripts.
> + However, due to how synthetic pointers are implemented, this is
> + always presented to us as a pointer type. This means we have to
> + sign-extend it manually as appropriate. Use raw
> + extract_signed_integer directly rather than value_as_address and
> + sign extend afterwards on architectures that would need it
> + (mostly everywhere except MIPS, which has signed addresses) as
> + the later would go through gdbarch_pointer_to_address and thus
> + return a CORE_ADDR with high bits set on architectures that
> + encode address spaces and other things in CORE_ADDR. */
> + bfd_endian byte_order = gdbarch_byte_order (get_frame_arch (frame));
> + LONGEST pointer_offset
> + = extract_signed_integer (value_contents (value),
> + TYPE_LENGTH (type), byte_order);
> +
> + return closure->get_location ().indirect_implicit_ptr (frame, type,
> + pointer_offset,
> + bit_offset, bit_length);
> +}
> +
> +/* Implementation of the coerce_ref method of lval_funcs for synthetic C++
> + references. */
> +
> +static value *
> +coerce_closure_ref (const value *value)
> +{
> + struct type *type = check_typedef (value_type (value));
> +
> + if (value_bits_synthetic_pointer (value, value_embedded_offset (value),
> + TARGET_CHAR_BIT * TYPE_LENGTH (type)))
> + {
> + computed_closure *closure
> + = (computed_closure *) value_computed_closure (value);
> + frame_info *frame = get_selected_frame (_("No frame selected."));
> +
> + return closure->get_location ().indirect_implicit_ptr (frame, type);
> + }
> + else
> + {
> + /* Else: not a synthetic reference; do nothing. */
> + return NULL;
> + }
> +}
> +
> struct piece_closure
> {
> /* Reference count. */
> --
> 2.17.1
>
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